Abstract: As a tertiary oil recovery technology, CO₂ miscrible flooding is generally implemented after water flooding, so that it is required to consider the impact of remaining injected water on CO₂ miscible flooding after water flooding. Based on the conventional PVT multiple-contact experiment, the long sand-filling tube with multi-point sampling holes was used to analyze the multi-phase and multi-component flow mechanisms in porous media and explore the influences of different water cut on the mass transfer of oil and gas through the gas injection and water alternating gas (WAG)injection experiments under different water cut stages. The experimental results show that CO₂ and crude oil can still be miscible at different water cut, and the CO₂ injection can open a new kind of flow channel to expand water flooding volume. However, the high water cut has a certain inhibitory effect on oil and gas mass transfer. Moreover, the conversion to CO₂ flooding at different water contents will lead to different flow and distribution characteristics of oil, water and gas in reservoir. The final recovery efficiency of gas flooding is mainly jointly affected by gas flooding efficiency and water flooding volume.